Introduction to GUI

GUI terms • The window that contains the GUI is called a frame. • The frame contains a panel that contains the controls that are

displayed by the application. • The panel in the Future Value Calculator interface contains ten

controls: four labels, four text fields, and two buttons. • Some text fields are not editable. They’re used to display output,

not to accept user input.

AWT and Swing components • The Abstract Window Toolkit (AWT) is an older technology for

creating GUIs that look and act a little different on different platforms.

• Swing is a newer technology that creates GUIs that are consistent from platform to platform.

• The AWT classes are stored in the java.awt package, while the Swing classes are stored in the javax.swing package. All Swing classes begin with the letter J.

The Component hierarchy

Container(abstract)

JComponent

JPanel Other Swingcomponents

Component(abstract)

Window

Frame

JLabel JTextField JButton

JFrame

A summary of the classes in the Component hierarchy Class Description Component An abstract base class that defines any object that can

be displayed. Container An abstract class that defines any component that can

contain other components. Window The AWT class that defines a window without a title

bar or border. Frame The AWT class that defines a window with a title bar

and border. JFrame The Swing class that defines a window with a title bar

and border. JComponent A base class for Swing components such as JPanel,

JButton, JLabel, and JTextField.

A summary of the classes in the Component hierarchy (continued) Class Description JPanel The Swing class that defines a panel, which is used to

hold other components. JLabel The Swing class that defines a label. JTextField The Swing class that defines a text field. JButton The Swing class that defines a button.

Set methods of the Component class Method Description setSize(intWidth, intHeight)

Resizes this component using two int values.

setLocation(intX, intY) Moves this component to the x and y coordinates specified by two int values.

setBounds(intX, intY,

intWidth, intHeight) Moves and resizes this component.

Notes • When you set the location and size of a component, the unit of

measurement is pixels, which is the number of dots that your monitor uses to display a screen.

• The preferred way to set the location of a component is to use a layout manager.

Set methods of the Component class (continued) Method Description setEnabled(boolean) If the boolean value is true, the

component is enabled. If false, the component is disabled, so it doesn’t respond to user input or generate events.

setVisible(boolean) Shows this component if the boolean value is true. Otherwise, hides it.

setFocusable(boolean) Determines whether or not this component can receive the focus.

setName(String) Sets the name of this component to the specified string.

Get methods of the Component class Method Description getHeight() Returns the height of this component as an int. getWidth() Returns the width of this component as an int. getX() Returns the x coordinate of this component as an int. getY() Returns the y coordinate of this component as an int. getName() Returns the name of this component as a String.

Other methods of the Component class Method Description isEnabled() Returns true if the component is enabled. isVisible() Returns true if the component is visible. requestFocusInWindow() Moves the focus to the component.

Common methods of the Frame class Method Description setTitle(String) Sets the title to the specified string. setResizable(boolean) If the boolean value is true, the user can

resize the frame.

A class that defines a frame class FutureValueFrame extends JFrame { public FutureValueFrame() { setTitle("Future Value Calculator"); setBounds(267, 200, 267, 200); setResizable(false); } }

A class that displays the frame import javax.swing.*; public class FutureValueApp { public static void main(String[] args) { JFrame frame = new FutureValueFrame(); frame.setVisible(true); } }

The setDefaultCloseOperation method of the JFrame class Method Description setDefaultCloseOperation(action) Sets the default close action

for the frame.

Constants to set the default close operation Constant Description JFrame.EXIT_ON_CLOSE Exits the application

when the user closes the window.

WindowConstants.DO_NOTHING_ON_CLOSE Provides no default action, so the program must explicitly handle the closing event.

WindowConstants.HIDE_ON_CLOSE Hides the frame when the user closes the window. This is the default action.

WindowConstants.DISPOSE_ON_CLOSE Hides and disposes of the frame when the user closes the window.

A class that defines a closeable frame class FutureValueFrame extends JFrame { public FutureValueFrame() { setTitle("Future Value Calculator"); setBounds(267, 200, 267, 200); setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); } }

Two methods of the Toolkit class Method Description getDefaultToolkit() A static method that returns the Toolkit

object for the current system. getScreenSize() Returns the screen resolution as a

Dimension object.

Two fields of the Dimension class Field Description height Stores the height of this Dimension object as

an int. width Stores the width of this Dimension object as

an int.

How to center a frame using the Toolkit class • The number of pixels per screen varies depending on the

resolution setting of the user’s monitor. • To determine the number of pixels for the current screen, you can

use a Toolkit object, or toolkit, to return a Dimension object that contains the number of pixels for the current screen.

• The Toolkit and Dimension classes are in the java.awt package.

A method that centers a frame on the screen private void centerWindow(Window w) { Toolkit tk = Toolkit.getDefaultToolkit(); Dimension d = tk.getScreenSize(); setLocation((d.width-w.getWidth())/2, (d.height-w.getHeight())/2); }

The constructor for a class that defines a centered frame

FutureValueFrame() { setTitle("Future Value Calculator"); setSize(267, 200); centerWindow(this); setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); }

How to add a panel to a frame • A JFrame object contains several panes. • To add components to a frame, you add them to the content pane

of the frame. • A panel is a component that’s used as a container for other

components. • The normal way to build a Swing user interface is to create a

panel, add components such as labels, text boxes, and buttons to the panel, then add the panel to the content pane.

Method needed to add components to the content pane with Java 5 Class Method Description JFrame add(Component) Adds a component to the frame’s

content pane.

A JFrame constructor that adds a panel to the content pane with Java 5

class FutureValueFrame() { setTitle("Future Value Calculator"); setSize(267, 200); centerWindow(this); setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); JPanel panel = new JPanel(); this.add(panel); }

Methods needed to add components to the content pane prior to Java 5 Class Method Description JFrame getContentPane() Returns a Container object that

represents the content pane. Container add(Component) Adds a component (such as a

JPanel) to this Container.

Code for adding a panel to the content pane prior to Java 5

Container contentPane = this.getContentPane(); contentPane.add(panel);

A frame with two buttons

Common constructors of the JButton class Constructor Description JButton() Creates a button with no text. JButton(String) Creates a button with the text specified by the

string.

Common methods of the JButton class Method Description setText(String) Sets the text of the button to the specified

string. getText() Returns a String object for the text of this

button.

A JPanel class with two buttons class FutureValuePanel extends JPanel { private JButton calculateButton; private JButton exitButton; public FutureValuePanel() { calculateButton = new JButton("Calculate"); this.add(calculateButton); exitButton = new JButton("Exit"); this.add(exitButton); } }

A frame constructor that adds the panel to the frame

class FutureValueFrame() { setTitle("Future Value Calculator"); setSize(267, 200); centerWindow(this); setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); JPanel panel = new FutureValuePanel(); this.add(panel); }

How to handle an action event 1. Specify that the class that contains the button implements the

ActionListener interface: class FutureValuePanel extends JPanel implements ActionListener

2. Add an ActionListener object to the button by calling the addActionListener method: exitButton.addActionListener(this);

3. Implement the ActionListener interface by coding the actionPerformed method: public void actionPerformed(ActionEvent e) { Object source = e.getSource(); if (source == exitButton) System.exit(0); }

A panel class that handles two action events class FutureValuePanel extends JPanel implements ActionListener { private JButton calculateButton; private JButton exitButton; public FutureValuePanel() { calculateButton = new JButton("Calculate"); calculateButton.addActionListener(this); // add an action listener this.add(calculateButton); exitButton = new JButton("Exit"); exitButton.addActionListener(this); // add an action listener this.add(exitButton); }

A panel class that handles two action events (continued) public void actionPerformed(ActionEvent e) { Object source = e.getSource(); if (source == exitButton) System.exit(0); else if (source == calculateButton) calculateButton.setText("Clicked!"); } }

Two panels that use the Flow layout manager

The setLayout method of the Container class Method Description setLayout(LayoutManager) Sets the layout manager for this

container.

Two constructors of the FlowLayout class Constructor Description FlowLayout() Creates a Flow layout with centered

alignment. FlowLayout(alignmentField) Creates a Flow layout with the

specified alignment.

Alignment fields of the FlowLayout class CENTER LEFT RIGHT

Code that creates the centered button panel class ButtonPanel extends JPanel { public ButtonPanel() { this.setLayout( new FlowLayout(FlowLayout.CENTER)); this.add(new JButton("Button One")); this.add(new JButton("Button Two")); this.add(new JButton("Button Three")); this.add(new JButton("Button Four")); this.add(new JButton("Button Five")); } }

Code that creates the right-aligned button panel class FutureValuePanel extends JPanel { private JButton calculateButton, exitButton; public FutureValuePanel() { this.setLayout(new FlowLayout(FlowLayout.RIGHT)); calculateButton = new JButton("Calculate"); this.add(calculateButton); exitButton = new JButton("Exit"); this.add(exitButton); } }

Two frames with panels that use the Border layout manager

Common constructor and method of the BorderLayout class Constructor Description BorderLayout() Creates a Border layout manager. Method Description add(Component, regionField) Adds the component to the

specified panel region.

Region fields of the BorderLayout class NORTH WEST CENTER EAST SOUTH

Code that creates the Border Layout frame class BorderLayoutPanel extends JPanel { public BorderLayoutPanel() { JButton button1 = new JButton("Button 1 (NORTH)"); JButton button2 = new JButton("Button 2 (WEST)"); JButton button3 = new JButton("Button 3 (CENTER)"); JButton button4 = new JButton("Button 4 (EAST)"); JButton button5 = new JButton("Button 5 (SOUTH)"); this.setLayout(new BorderLayout()); this.add(button1, BorderLayout.NORTH); this.add(button2, BorderLayout.WEST); this.add(button3, BorderLayout.CENTER); this.add(button4, BorderLayout.EAST); this.add(button5, BorderLayout.SOUTH); } }

Code that creates the Future Value Calculator frame class BorderLayoutPanel extends JPanel { public BorderLayoutPanel() { this.setLayout(new BorderLayout()); JPanel buttonPanel = new JPanel(); buttonPanel.setLayout( new FlowLayout(FlowLayout.RIGHT)); JButton calculateButton = new JButton("Calculate"); JButton exitButton = new JButton("Exit"); buttonPanel.add(calculateButton); buttonPanel.add(exitButton); this.add(buttonPanel, BorderLayout.SOUTH); } }

Two panels that display labels

Common constructors and methods of the JLabel class Constructor Description JLabel() Creates a blank label. JLabel(String) Creates a label with the text specified by the string. Method Description getText() Returns the text in this text field as a String. setText(String) Sets the text in this field to the specified string.

How to work with labels • The JLabel class defines a label component that can be used to

display text on the panel. • If you need to refer to a label in code, you can (1) assign it to a

variable and then add that variable to the panel or (2) create the label and add it to the panel in a single statement.

A class that creates the Label One panel class LabelPanel extends JPanel { private JLabel labelOne; public LabelPanel() { labelOne = new JLabel("Label One"); this.add(labelOne); } }

A class that creates the Future Value panel class FutureValuePanel extends JPanel { public FutureValuePanel() { this.setLayout(new FlowLayout(FlowLayout.RIGHT)); this.add(new JLabel("Monthly Payment:")); this.add(new JLabel("Yearly Interest Rate:")); this.add(new JLabel("Number of Years:")); this.add(new JLabel("Future Value:")); } }

Two versions of a panel that displays two text fields

Common constructors of the JTextField class Constructor Description JTextField(intColumns) Creates a text field with the

specified number of columns. JTextField(String, intColumns) Creates a text field that starts

with the text specified by the string and contains the specified number of columns.

Common methods of the JTextField class Method Description getText() Returns the text in this text field as a String

object. setText(String) Sets the text in this field to the specified

string. setColumns(intSize) Sets the number of columns to the

specified value. setEditable(boolean) Determines whether or not the field can be

edited. setFocusable(boolean) Determines whether or not the field can

receive the focus.

A class that creates the panel with two text fields class TextFieldPanel extends JPanel { private JTextField textFieldOne, textFieldTwo; public TextFieldPanel() { textFieldOne = new JTextField("Test", 20); this.add(textFieldOne); textFieldTwo = new JTextField(10); this.add(textFieldTwo); } }

Code that modifies the second text field public void modifyFields() { String data = textFieldOne.getText(); textFieldTwo.setText(data); textFieldTwo.setColumns(20); textFieldTwo.setEditable(false); }

The panels of the user interface for the Future Value Calculator application

FutureValuePanel

displayPanel

buttonPanel

The Future Value Calculator application import java.awt.*; import java.awt.event.*; import javax.swing.*; import java.text.*; public class FutureValueApp { public static void main(String[] args) { JFrame frame = new FutureValueFrame(); frame.setVisible(true); } }

The Future Value Calculator application (cont.) class FutureValueFrame extends JFrame { public FutureValueFrame() { setTitle("Future Value Calculator"); setSize(267, 200); centerWindow(this); setResizable(false); setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); JPanel panel = new FutureValuePanel(); this.add(panel); } private void centerWindow(Window w) { Toolkit tk = Toolkit.getDefaultToolkit(); Dimension d = tk.getScreenSize(); setLocation((d.width-w.getWidth())/2, (d.height-w.getHeight())/2); } }

The Future Value Calculator application (cont.) class FutureValuePanel extends JPanel implements ActionListener { private JTextField paymentTextField, rateTextField, yearsTextField, futureValueTextField; private JLabel paymentLabel, rateLabel, yearsLabel, futureValueLabel; private JButton calculateButton, exitButton; public FutureValuePanel() { // display panel JPanel displayPanel = new JPanel(); displayPanel.setLayout( new FlowLayout(FlowLayout.RIGHT));

The Future Value Calculator application (cont.) // payment label paymentLabel = new JLabel("Monthly Payment:"); displayPanel.add(paymentLabel); // payment text field paymentTextField = new JTextField(10); displayPanel.add(paymentTextField); // rate label rateLabel = new JLabel("Yearly Interest Rate:"); displayPanel.add(rateLabel); // rate text field rateTextField = new JTextField(10); displayPanel.add(rateTextField); // years label yearsLabel = new JLabel("Number of Years:"); displayPanel.add(yearsLabel);

The Future Value Calculator application (cont.) // years text field yearsTextField = new JTextField(10); displayPanel.add(yearsTextField); // future value label futureValueLabel = new JLabel("Future Value:"); displayPanel.add(futureValueLabel); // future value text field futureValueTextField = new JTextField(10); futureValueTextField.setEditable(false); futureValueTextField.setFocusable(false); displayPanel.add(futureValueTextField); // button panel JPanel buttonPanel = new JPanel(); buttonPanel.setLayout( new FlowLayout(FlowLayout.RIGHT));

The Future Value Calculator application (cont.) // calculate button calculateButton = new JButton("Calculate"); calculateButton.addActionListener(this); buttonPanel.add(calculateButton); // exit button exitButton = new JButton("Exit"); exitButton.addActionListener(this); buttonPanel.add(exitButton); // add panels to main panel this.setLayout(new BorderLayout()); this.add(displayPanel, BorderLayout.CENTER); this.add(buttonPanel, BorderLayout.SOUTH); }

The Future Value Calculator application (cont.) public void actionPerformed(ActionEvent e) { Object source = e.getSource(); if (source == exitButton) System.exit(0); else if (source == calculateButton) { double payment = Double.parseDouble( paymentTextField.getText()); double rate = Double.parseDouble( rateTextField.getText()); int years = Integer.parseInt( yearsTextField.getText()); double futureValue = FinancialCalculations.calculateFutureValue( payment, rate, years); NumberFormat currency = NumberFormat.getCurrencyInstance(); futureValueTextField.setText( currency.format(futureValue)); } } }

Introduction to GUI

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